After the last tourists leave the Church of the Holy Sepulcher in Jerusalem’s Old City at nightfall, a little-known but centuries-old tradition unfolds at one of Christianity’s holiest sites.

Clerics from the three largest denominations represented in the church — Greek Orthodox, Armenian and Roman Catholic — gather each night for special prayers reserved for the men who take care of the site where Christians believe Jesus was crucified, buried and resurrected.

Starting at midnight, clerics and monks sing and pray for hours, their chants echoing through the cavernous chambers of the Holy Sepulcher’s darkest rooms.

"The door of the church is closed, no pilgrims, no tourists, it’s very quiet," said Father Isidoros Fakitsas, the superior of the Greek Orthodox Patriarchate at the church. "It’s amazing to feel the liturgy with no people, only the monks."

Isidoros said he has attended the services for 21 years.

The preparations require a rigid routine. Before the first prayers of the new day, the Christian shrine needs to be cleaned, and maintenance work has to be done.

The clerics sweep the floors, replace oil lamps and clean candle holders, after thousands of pilgrims visited throughout the previous day. Occasionally a small number of devoted pilgrims help them with the cleanup and are permitted to stay and pray inside the church all night.

The early morning mass is a tradition associated with monastic life, said Father Eugenio Alliata, professor of Christian Archaeology at the Studium Biblicum Franciscanum in Jerusalem.

"Mostly monks and religious people want to pray not only all the day, but also all the night, or part of the day or part of the night. It is part of the desire to pray without ceasing because prayers to God must be given all the time, day and night," Alliata said.

Father Fergus Clarke, the guardian for the Franciscan community inside the Holy Sepulcher, said the night prayers require a certain amount of personal sacrifice, but also bring greater spiritual fulfillment. "That’s a wonderful vocation ... to be able to do something like that, to know that while people are sleeping, others are praying," he said.

The night liturgies inside the Holy Sepulcher are regulated by a consolidated tradition: The Greek-Orthodox start to celebrate mass inside Jesus’ Tomb at 12:30 a.m., before handing over to the Armenians and then the Franciscans. The Greek Orthodox liturgy at the tomb is the longest, lasting for about three and a half hours; the Armenians then take over for an hour and a half and the Franciscans for another half hour.

The night service is subject to some variations. On the feast of Saint Matthias on the morning of May 14, for example, Catholics lead a procession to Jesus’ tomb during the Greek Orthodox liturgy.

Sounds collided with one another that night. The celestial voices of Armenian priests rose from their wing of the Church as the sound of a Franciscan pipe organ came from the opposite direction.

Competing for attention is nothing new in the ancient church.

The three main denominations that share the church jealously guard their turf, and an air of mistrust lingers as each group makes sure no one else crosses into their space.

While the Tomb of Jesus and the main passages of the Holy Sepulcher are considered common spaces, the three main religious communities each own a part of the church: The Chapel of Saint Helen, near the place where Jesus’ cross is said to have been found, belongs to the Armenians; the Greek-Orthodox Church has ownership over the largest part of the church, including the Altar of the Calvary, where Jesus’s cross was raised; the Franciscans own the Chapel of the Crucifixion where Jesus was crucified, along with the northern part of the Church, where according to tradition Jesus appeared to his mother.

The church was first built by Roman Emperor Constantine in 325, at the site where the tomb of Jesus was believed to have been found.

Constantine’s structure was destroyed in 1009 by Muslim Caliph al-Hakim.

A 12th century restoration by the Crusaders gave the Holy Sepulcher its current appearance.

Life inside the Holy Sepulcher is regulated by a complex maze of norms that are often subject to different interpretations, said Father Samuel Aghoyan, the Armenian Superior of the Holy Sepulcher.

At times, tensions have even spilled over into violence, with monks pushing and punching each other.

"We keep almost awake at night here to see that things are done properly, on time, that no one will trespass the other’s right by doing things that he’s not supposed to do," said Father Samuel.